The games the airlines play with fares, clssses and dates make this a very annoying topic.
A recent trip from EWR to SFO for business - leave Thursday evening, come back Saturday evening at 9pm - full fare on CO $1,800. If I stay in SFO and have dinner with friends - fly back at 1am connect through IAH - fare drops to $350.
I'll always book the cheapeast fare that works with my needs (company policy) so I'm really at the mercy of the fare structure and availability.
Dave